The overall objective of this proposed research is to develop near-infrared imaging for the detection and diagnosis of early dental caries (dental decay). New, more sophisticated diagnostic tools are needed for the detection and characterization of caries lesions in the early stages of development. If carious lesions are detected early enough, before cavitation, then they can be arrested/remineralized by non-surgical means through fluoride therapy, anti-bacterial therapy, dietary changes, or by low intensity laser irradiation. The principal factor limiting optical transmission through the tooth i the visible range from 400-700-nm is light scattering in sound enamel and dentin. The magnitude of light scattering decreases markedly at longer wavelengths in the near infrared due to the size of the principal light scatterers in enamel. The central hypothesis of this proposal is that the near-IR (NIR) region between 1300 and 1700-nm offers the greatest potential for new optical imaging modalities due to the weak scattering and absorption in sound dental hard tissue. The overall objectives of this proposal will be achieved through the following specific aims: (1) To test the hypothesis that the maximum contrast between sound and demineralized enamel in NIR reflectance measurements lies in the wavelength regions coincident with weak light scattering in enamel and strong water absorption, (2) To test the hypothesis that NIR imaging on proximal and occlusal surfaces can used for improved assessment of caries lesions for clinical screening, (3) To test the hypothesis that a NIR imaging system can be used for improved discrimination of composite sealants and restorations from sound and demineralized tooth structure. It is likely that if these studies and future clinical trials are a success, that his novel technology for imaging dental hard tissue will be employed for the detection and monitoring of early carious lesions without the use of ionizing radiation, thereby enabling conservative non-surgical intervention and the preservation of healthy tissue structure.